1. Field of the Invention
The present invention relates to a stacker crane.
2. Description of the Related Art
A conventional automated warehouse includes, for example, a pair of racks, a stacker crane, a warehousing station, and a delivery station. The pair of racks is spaced apart by a prescribed spacing in the forward-rearward direction. The stacker crane is provided moveably in the left-right direction between the front and rear racks. The warehousing station is disposed on a side of one of the racks. The delivery station is disposed on a side of the other one of the racks. The racks have numerous article storage shelves at the top, bottom, left, and right.
The stacker crane includes a travelling truck, a lift platform that is freely elevatable along a mast provided to the travelling truck, and an article transfer apparatus (e.g., a slide fork that is slidably provided in the forward-rearward direction) that is provided to the lift platform.
The travelling truck includes drive wheels and a travelling motor. The drive wheels are located on front and rear potions in a travelling direction of the stacker crane, and the travelling motor is located above the drive wheels (e.g., refer to Japanese Unexamined Patent Application Publication No. 2008-63067).
In recent years, there has been a demand to achieve high performance in stacker cranes (high speed performance and high acceleration-deceleration performance of the crane). Furthermore, achieving such performance also increases the possibility of wheel slippage, therefore it becomes necessary to pressurize the wheels. However, it becomes difficult to set the pressurizing force due to the variations in wheel pressure if the system uses the drive wheels which support the weight of the whole stacker crane.